A display device using a liquid crystal panel or the like is recently utilized in various fields including a television, a car navigation system, and a computer, in view of its light weight, thin, and low power consumption. Specifically, as a demand for display quality of the liquid crystal panel is increased every year, employing a mode of driving the liquid crystal panel in an increased contrast and a widened view angle becomes a mainstream.
Specifically, an IPS (In-Plane Switching; hereinafter referred to as IPS) drive mode is superior in view of the above-described properties, liquid crystal manufacturing companies employing the above drive mode are increased.
The general liquid crystal panel of the IPS drive mode includes a pair of substrates facing each other, and a gap between the substrates is constantly maintained by a spacer, and the gap is filled with liquid crystal molecules. One of the substrates is a an active matrix type TFT array substrate including pixel electrodes, which is arranged in a region formed in a matrix shape by a gate wiring and a source wiring, and a TFT, which is formed at an intersection of both wirings, and a counter electrode formed on the same substrate. The drive of the liquid crystal molecules is controlled by electric charges accumulated between the pixel electrode and the counter electrode.
The other substrate facing the above TFT array substrate is an opposite substrate including a color filter (hereinafter referred to as CF). The opposite substrate is provided with a black matrix shielding a domain region of the liquid crystal molecules, a coloring material layer, an organic film layer, and a columnar spacer, and a conductive film is generally not formed. The IPS drive mode realizes the highly widened view angle by forming the pixel electrodes and the counter electrode on the same substrate (TFT array substrate), and generating an electric field in a parallel direction with respect to both substrates to move the liquid crystal molecules in a horizontal direction.
As a drive mode further evolved from the IPS drive mode, an FFS (Fringe Field Switching; hereinafter referred to as FFS) mode is being developed. A difference between the liquid crystal panels of the IPS drive mode and the FFS mode is that an insulating film is interposed between the pixel electrode and the counter electrode to form an another layer, and an electric field is generated in a more horizontally direction along a substrate planar direction when a voltage is applied, thereby further realizing the increased contrast and the widened view angle.
According to the FFS drive mode, since the insulating film is interposed between the pixel electrode and the counter electrode to form another layer, as described above, the number of masks is increased when each electrode is formed by patterning, which increases its cost. Therefore, to reduce the number of masks, a method of eliminating the insulating film between the source wiring and the pixel electrode and forming the source wiring and the pixel electrode on the same layer may be used. (see JP-A-2011-107678 (page 8 and FIG. 6))